Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$224.84	3.870%	$233.5413	$233.54	$233.55	$233.50
Purchase #2	$176.38	8.631%	$191.6034	$191.60	$191.60	$191.60
Purchase #3	$53.96	12.690%	$60.8075	$60.81	$60.80	$60.80
Purchase #4	$208.50	7.398%	$223.9248	$223.92	$223.90	$223.90
Purchase #5	$198.41	12.702%	$223.612	$223.61	$223.60	$223.60
Purchase #6	$112.89	9.475%	$123.5863	$123.59	$123.60	$123.60
Purchase #7	$32.29	11.397%	$35.9701	$35.97	$35.95	$36.00
7 purchase totals =	$1,007.27		$1,093.0454	$1,093.04	$1,093.00	$1,093.00